How Do I Stop a Rooflight Overheating a Room in Summer?

A rooflight overheats a room because it points at the sky. A wall window sees the horizon and catches the sun at a low angle for part of the day. A rooflight, and a skylight on a low-pitched roof in particular, faces the high summer sun more directly and for longer. Sunlight passes through clear glass, lands on the floor and furniture, and turns to heat. The glass then stops that heat getting out again.

The air does the rest. Warm air rises, and a loft room or an extension with a high ceiling collects it right under the glazing. That is why a top-floor room with a skylight can feel stuffy in July while the rest of the house is fine. Summer heat gain is the only subject here; for the full range of heat and insulation questions, start at our energy efficient rooflights page.

The direction a rooflight faces changes the problem more than any other factor. A south-facing slope takes the strongest sun through the middle of the day. West-facing glass catches the late afternoon and evening sun, which lands just when a bedroom or living room is warmest. East-facing glass heats up early but has usually cooled by the evening. North-facing glass stays coolest and gives the steadiest light.

That gives you a choice at the planning stage. If a roof has two slopes, a rooflight on the north or east side often gives plenty of daylight with far less heat. Where the only usable slope faces south or west, the glass specification and the shading matter much more. We look at the aspect of every roof at the survey, because it changes what we recommend.

This is the part you can build into the unit itself. Solar control glass carries a coating that reflects part of the sun's heat while still letting most of the daylight through. Some units use a tint in the glass or the laminated layer instead, which absorbs more of the heat. Both lower how much of the sun's energy reaches the room, and both can leave the glass slightly less bright or a little tinted when you look through it.

The trade-off to know about is winter. A coating chosen to keep the sun out also keeps out some of the free warmth you would welcome in January. For a room that overheats in summer and stays comfortable otherwise, the exchange is usually worth making. For a north-facing rooflight it can be needless. The glass is rated by its g-value, which is the share of solar energy that gets through, and a lower g-value means less heat gain. Ask for that figure in your quote, alongside the U-value.

What the glass does in January is a separate question, answered in does a rooflight make a room colder in winter.

Glass control only goes so far, because some heat always gets in. An opening rooflight lets that heat out. Warm air rises, so a rooflight at the top of the room is the natural exit. Open it with a window lower down or on another side of the house, and air moves through on its own, which is called stack ventilation.

The effect is strongest in a loft conversion or a tall kitchen extension, where the opening sits well above head height. In those rooms, a fixed rooflight with no way to vent is a poor choice if overheating is likely. Some electric and solar opening units can be set to open on a warm day, which helps when nobody is home to do it. How these units move air is explained in opening rooflights for ventilation, while the models we supply and fit are listed under electric opening rooflights.

A blind is the simplest part of the answer and often the most effective. The best place for it is outside, because it stops the sun before it passes through the glass. An external blind or awning-style screen can make a large difference to the heat entering the room. An internal blind works less well, because the heat has already come through the glass by the time the blind meets it, though it does still reduce glare and some warmth.

Roof windows have their own matching blinds from the maker, which slide in channels on either side of the frame. Reflective-faced blinds do better against summer sun than dark fabrics.

• Check which way the slope faces before choosing the glass
• Ask for the g-value as well as the U-value
• Choose an opening unit where the room is high or on the top floor
• Plan for a blind, outside if the unit allows it

Nothing is priced until we have been up and looked at the roof, noting its aspect, the ceiling height and how the room is used. A bedroom that overheats at night needs a different answer from a kitchen that gets the sun at lunchtime. You then receive a fixed-price quote on paper, and the installation carries a 10-year guarantee that is put in writing too. The Building Regulations 2010 class both fitting a new rooflight and replacing one as controlled work. Notifiable jobs are reported to Building Control by us. Message us on WhatsApp, or use the form to get a free quote.